The invention relates to processes for the commercially practical production of radiopharmaceutical activities and, more particularly, relates to a process for the production of astatine-211 (At-211).
For about the last forty years, there has been an interest in exploring the potential of At-211 for therapeutic biomedical applications. At-211 decay results in nearly pure alpha particle emissions. The radiotoxicity associated with such alpha particle emissions and the associated emissions resulting from the decay of its daughter, polonium-211 (Po-211), which has a half-life of only about 0.56 seconds, led to early recognition of the potential for such beneficial therapeutic applications.
At-211 has a half-life of 7.21 hours, which is sufficiently long to enable its practical production, chemical synthesis, transportation, quality control and appropriate biological application in a number of useful radiopharmaceutical treatments of certain diseases. Heretofore, research and development work relating to such radiopharmaceutical treatment procedures has largely focused on the preparation and in vivo evaluation of labelled antibodies, proteins, drugs and inorganic colloids. Such research has usually concentrated on the production of At-211 as a source of Astatine for studies of the physical and chemical properties of the element.
In addition to the interest generated by the established and potential uses of At-211 in therapeutic radiopharmaceuticals, increasing attention is being received by At-211 due to its potential use in radiation synovectomy and for fundamental studies in cell biology. It has been demonstrated, for example, that At-211 Tellurium-colloid can be curative, without undue toxicity, in mice bearing Ascites tumor cells. Among currently available alpha particle emitters, At-211 is particularly promising for radiopharmaceutical therapeutic uses, because it decays by a double branched pathway into lead (Pb-207), directly by alpha emission, and indirectly through electron capture into polonium (Po-211), which in turn decays almost spontaneously by alpha emission.
In the past, radiochemical separation of At-211 has been found to be generally unreliable due to the low and variable recovery yields attainable with such processes. If an At-211 radiopharmaceutical is to be developed for clinical application, it will be necessary to develop a production process in which small controlled volumes of At-211, in specified chemical forms, can be produced more reliably and consistently. Preferably, such a process would be readily controllable to produce desirable small volumes of selected activities in a solution of solvents that is compatible with preselected radiopharmaceutical procedures in which the activities are to be used. More specifically, it would be desirable to have such a process in which a choice of solvents can be effectively used in the production of a desired At-211 radiopharmaceutical.